金川岩浆铜镍(铂)硫化物矿床铂族金属富集过程及富集机制
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Enrichment processes and mechanism of platinum group element in Jinchuan magmatic Cu- Ni (PGE) sulfide deposit
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    摘要:

    金川岩浆铜镍(铂)硫化物矿床是我国最主要的铂族等战略性关键金属宝库。金川矿床中铂族金属的富集过程和富集机制还存在很多争论。本文通过详细的矿物学及矿床学研究,厘定了金川矿床成矿阶段。成矿阶段可划分为硫化物矿浆结晶阶段、挥发分流体作用阶段及热液改造阶段。其中硫化物矿浆结晶阶段的主要矿物组合为镍黄铁矿(Pn- a)- 磁黄铁矿(Po- a)- 黄铜矿(Ccp- a);挥发分流体作用阶段的主要矿物组合为镍黄铁矿(Pn- b)- 磁黄铁矿(Po- b)- 黄铜矿(Ccp- b)- 黄铁矿(Py- Ⅰ)- 磁铁矿(Mag- Ⅰ)- 菱铁矿- 叶蛇纹石- 磷灰石- 铬铁矿- 白云石- 方解石(Cal- Ⅰ)- 金云母。热液改造阶段的矿物组合为透闪石- 绿泥石- 蛇纹石- 方解石(Cal- Ⅱ)- 磁铁矿(Mag- Ⅱ)。高倍电子探针镜下发现,金川矿床铂族矿物与磁铁矿(Mag- Ⅰ)、黄铁矿(Py- Ⅰ)、铬铁矿、磷灰石、黄铜矿、磁黄铁矿、镍黄铁矿及菱铁矿等共生。金川铜镍硫化物矿床中铂族元素(PGM)矿物主要包括硫砷铱矿(IrAsS)、钯的铋化物、碲化物和硒化物、钯的金属互化物(PdAu2)、砷铂矿(PtAs2)、铂单质以及铂的金属合金(Pt- Fe)。其中大量的PGM分布于镍黄铁矿的裂隙中,或产于镍黄铁矿、磁黄铁矿及蛇纹石裂隙中。与磁铁矿、菱铁矿、铬铁矿、黄铜矿、磷灰石以及叶蛇纹石等矿物共生,指示PGE富集与氧化性流体加入密切相关。金川矿石镍黄铁矿(Pn- b)、磁黄铁矿(Po- b)、黄铜矿(Ccp- b)、黄铁矿(Py- Ⅰ)、磁铁矿(Mag- Ⅰ)以及菱铁矿中高Co含量,表明流体在Co的超常富集过程中也起到了决定性作用。金川矿石中大量碳酸盐矿物、叶蛇纹石、金云母、磁铁矿、黄铁矿、铬铁矿以及富Cl磷灰石的出现;S、Mg元素呈网脉状分布于蚀变橄榄石和硫化物中,推测流体组分可能是一种富C富Cl的富含挥发分的高氧逸度流体。金川铬铁矿、磁铁矿(Ⅰ)、菱铁矿等矿物中高Ti、高Nb含量和高Nb/Ta比值,暗示此流体可能是一种高温的超临界流体。以上特征综合表明该特征流体对金川铜镍硫化物矿床中铂族元素等关键金属的超常富集起到了关键控制作用。当挥发分流体与残余硫化物矿浆相互作用及改造先存硫化物及橄榄石时,不仅会促使Os、Ir、Ru、Rh、Pt、Pd进一步活化、富集,还会导致流体中PGE强烈富集,使得流体中的Pd、Se、Te、Bi、Pt含量不断提高,最终形成大量的PGM。综上所述,本文认为在岩浆演化晚期可能存在一种高氧逸度的富Cl富C的深源流体注入岩浆房,该深源挥发分流体对PGE及Co的迁移和超常富集起到了关键控制作用。

    Abstract:

    The Jinchuan magmatic Cu- Ni (PGE) sulfide deposit is the most important strategic metal treasure- house of platinum group. The enrichment process and mechanism of platinum group metals (PGEs) in Jinchuan deposit are still controversial. Based on detailed mineralogical and deposit studies, it is found that the mineralization stage of Jinchuan deposit can be divided into sulfide melt crystallization stage, interaction stage of volatile fluid- sulfide melt and hydrothermal alteration stage. The mineral paragenetic assemblages in the sulfide melt crystallization stage are pentlandite (Pn- a)+pyrrhotite (Po- a)+chalcopyrite (Ccp- a). The mineral paragenetic assemblages in the interaction stage of volatile fluid- sulfide melt are pentlandite (Pn- b)+pyrite (Py- Ⅰ)+chalcopyrite (Ccp- b)+magnetite (Mag- Ⅰ)+siderite+serpentine+apatite+dolomite+calcite (Cal- Ⅰ)+phlogopite. In the hydrothermal alteration stage, the mineral paragenetic assemblages are tremolite+chlorite+serpentine+calcite (Cal- Ⅱ)+magnetite (Mag- Ⅱ). It is found that platinum group minerals are paragenetic with magnetite (Mag- Ⅰ), pyrite (Py- Ⅰ), chromite, chalcopyrite (Ccp- b), apatite, pentlandite, pyrrhotite and siderite in Jinchuan deposit under high- power electron probe microscopy. The study of PGMs in Jinchuan Cu- Ni sulfide deposit shows that the types of PGM include sulfoarsenide (IrAsS), bismuth of palladium, telluride and selenide of palladium, metal complexes of palladium (PdAu2), platinum and its metal alloy (Pt- Fe). Among them, most PGMSs are distributed in the cracks of pentlandite, pyrrhotite and altered olivine, and paragenetic with magnetite, siderite, chromite, chalcopyrite, apatite and antigorite, indicating that PGE enrichment is closely related to fluid addition. The high contents of Co in Pn- b, Ccp- b, Py- Ⅰ, Mag- Ⅰ and siderite in Jinchuan ores indicates that fluid also plays a decisive role in the super- enrichment of Co. The occurrence of a large number of carbonate minerals, antigorite, phlogopite, magnetite, pyrite, chromite and Cl- rich apatite in the Jinchuan ores, S and Mg elements are distributed in olivine and sulfide in net- vein. It is speculated that the fluid component may be a C- rich and Cl- rich fluid with high oxygen fugacity. The high contents of Ti and Nb and Nb/Ta ratio of chromite, magnetite- Ⅰ, siderite and other minerals in the Jinchuan deposit suggest that the fluid may be a high- temperature supercritical fluid. The above characteristics indicate that this fluid plays a key role in controlling the super- enrichment of PGE and other key metal elements in the Jinchuan Cu- Ni sulfide deposit: when the volatile fluid interacted with the residual sulfide melt and altered the preexisting sulfide and olivine, it not only promotes the further activation and enrichment of Os, Ir, Ru, Rh, Pt and Pd, but also leads to the strong enrichment of PGE in the fluid, which increases the content of Pd, Se, Te, Bi and Pt in the fluid, and finally forms most PGMs. In conclusion, we conclude that there may be an acidic, high oxygen fugacity, Cl- rich and C- rich derived from deep mantle fluid in the late stage of magma evolution, which plays a key role in controlling the migration and super- enrichment of PGE and Co.

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陈学根,苏尚国,施南,王跃,张雅南,郝金华,刘翠,杨宗锋.2023.金川岩浆铜镍(铂)硫化物矿床铂族金属富集过程及富集机制[J].地质学报,97(11):3715-3736.
CHEN Xuegen, SU Shangguo, SHI Nan, WANG Yue, ZHANG Yanan, HAO Jinhua, LIU Cui, YANG Zongfeng.2023. Enrichment processes and mechanism of platinum group element in Jinchuan magmatic Cu- Ni (PGE) sulfide deposit[J]. Acta Geologica Sinica,97(11):3715-3736.

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  • 收稿日期:2023-04-27
  • 最后修改日期:2023-05-17
  • 录用日期:2023-05-22
  • 在线发布日期: 2023-12-09
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